The watthour meter test equipment sockets used today in most portable test equipment trace their heritage either from stationary test equipment or from portable meter socket adapters.
Stationary test equipment includes commercially available meter sockets of the general types available from Millbank, Durham, Siemens, General Electric, Eaton, Cooper and many others, as well as certain specially designed test meter sockets that have been used in such stationary test equipment as the Radian Research, Inc. RFL 5800 and UTEC 622, the Watthour Engineering Company, Inc. WECO 2300, and the Testcor Inc. MTS3000.
Commercially available meter sockets generally are not well adapted to the portable applications. Because of their application, socket weight, connector cycle life, and short cable routing are very low on the design criteria for these kinds of sockets. They were originally designed to protect a sealed meter in a stationary application with a limited number of insertions over its lifetime. They either come with a relatively heavy steel case or are intended to be mounted into a steel housing to protect them. Cycle life of the contacts is generally expected to under several hundred insertions and removals over the life of the socket. Typical meter socket connectors are illustrated in FIGS. 1a and 1b. 
The high current carrying connectors of such sockets need low resistance contact to the current carrying blades of the meter. As a result, such connectors are usually designed to have an aggressive wiping action, and, if possible, to bite into the metal of the blade. This provides more certainty of sound electrical connection in the presence of potentially dirty meter connector blades. As a result of this feature, the connectors wear quickly and can create metal debris that stays in the meter socket housing.
A major exception to very limited connector lifetime is the lever bypass socket. These sockets have lever actuated current carrying connectors that provide nearly zero-force insertion of the meter. This is achieved by having the lever spread the contacts holding the current leads of the meter. The contact comprises a stationary jaw half supporting a movable jaw half which pivots on a pin through the movable jaw half and the stationary jaw half. When the lever is released, a spring closes the movable jaw half against the stationary jaw half, capturing the meter blade between them. This is illustrated in FIG. 2.
However, the lever bypass socket current connector provides no wiping action for the current carrying meter blade. The lever bypass socket current connector relies upon a large side pressure action against the meter blade to make low resistance contact to the meter blade. Thus, to make proper contact, the inserted meter blade must be relatively clean of oxide, and free of greases, residues and debris. The majority of the current flows through the stationary jaw half, since the movable jaw half is coupled to the stationary jaw half through the pivot pin which adds resistance to the current path through the movable jaw half to the conductor coupled to the stationary jaw half. The lever bypass connector is also difficult to clean.
The potential and other low current contacts such as KYZ contacts usually remain a scaled down version of the typical connector illustrated in FIG. 1. In some cases, a spring-loaded retractable button, FIG. 3a, or “pogo” pin, FIG. 3b, is used to contact to the end of the contact blade.
The lifetime of the lever bypass socket is generally longer than the typical meter socket, because the lever bypass socket was designed with the idea that the meter might be removed for testing more frequently, for example, on a monthly basis. However, the lever bypass socket was not designed for the test equipment market, where dozens of meters a day can be inserted into the socket for testing. Replacement of contacts in these sockets usually requires significant effort, as the sockets were not designed with field replacement of the components in mind.
Test meter sockets such as those incorporated into the above-identified equipment were designed specifically for use in stationary test equipment. As a result, those sockets have been designed to take the abuse of repeated insertions and removals. They use zero insertion force current blade connectors similar to those found in lever bypass meters, but generally have much higher clamping forces to the meter blade than are found in the lever bypass socket. Instead of a lever to open the current connection and a spring to close the current connection, the current connection clamping is generally driven by a motor or solenoid with a greater force than found in the lever bypass socket. Also, the current connection clamping is frequently activated automatically or semi-automatically. The electrical potential connections are usually by means of a retractable button or pin similar to the button action described in the lever bypass socket described above with the connection made to the end of potential connection blade.
These meter sockets have improved the lifetime of commercial sockets. However, because they are designed for tens of thousands of meter insertions and removals over their useful lifetimes, they have higher connection pressures in their current connections, and have a motor or solenoid, these meter sockets are even heavier than their commercially available counterparts. These designs have improved socket lifetime in exchange for increased complexity and weight. Additionally, as these meter sockets were intended for stationary application where size, weight and complexity are not major issues, they have not addressed minimizing routing of current-carrying wire to reduce wire weight and volt-ampere (hereinafter sometimes VA) drive required to test a meter.
Currently available portable meter socket adapters are somewhat better adapted to the portable test equipment market, since the designers focus on weight as a primary consideration. Ekstrom and Marwell are two manufacturers of currently available portable meter socket adapters. Originally these adapters aided field testing of meters with load boxes and reference standards by adapting meter blades and meter sockets to standard connection points for the test equipment. Depending upon what meter configurations were being tested during the day, the field tester might have to carry several different meter socket adapters. Weight was consequently an issue.
These socket adapters typically contain both meter socket connectors on the front side, FIGS. 4a and 4b, and meter blades on the back side, FIG. 4b. 
The connectors are similar in form to the connectors illustrated in FIG. 1, but are typically made using sturdier materials and methods to improve useful life.
The current trend is away from carrying several pieces of gear and combining load box, reference standard and adapter socket into one piece of portable test gear that can service many, and preferably all, of the S-base meter forms. System weight, service life, ease of maintenance, and robustness in a rugged operating environment are of primary importance.
The Powermetrix PowerMaster 4 series automated meter tester is an example of equipment using meter sockets adapted from stationary equipment. Examples of equipment using adaptations of these meter socket adapters for the meter socket in the test equipment are the Radian RM-17 portable watt hour test system and the Probewell MT-1 Series of portable watthour meter testers.
The disclosures of all of these prior art meters are hereby incorporated herein by reference. This listing is not intended as a representation that a complete search of all relevant prior art has been conducted, or that no better references than those listed exist. Nor should any such representation be inferred.